Objective All-fiber, high-power lasers play important roles in practical applications and scientific research. In the research field of high-power pulsed fiber lasers, the master oscillator power amplifier (MOPA) configuration seeded by a pulsed fiber laser oscillator is a typical design, which is widely used to achieve high-power pulsed laser emission. However, there still exist too many factors influencing the practical realization of such devices, such as 1) nonlinear effects, especially stimulated Raman scattering (SRS), 2) overly high intrinsic temperature of the active fiber caused by quantum loss, 3) parasitic oscillation induced by gain saturation, and 4) fiber damage due to instantaneous and violent pulsed power peaks. Appropriate fiber design can mitigate these effects to some degree. The realization of more than ten thousand watts in continuous-wave lasers based on homemade fibers has been reported. However, the fiber damage requires more attention in pulsed fiber lasers because of their high peak powers. Currently, most active fibers utilized in a high-power pulsed-laser system rely on imports. In this paper, we report the realization of a 1000W nanosecond pulsed laser using homemade double-cladded Yb-doped fibers (DCYDFs). To our knowledge, this is the first fiber laser based on homemade fibers to break through the kilowatt level in average power.
Methods We construct an acousto-optic-modulator-based seed source with a tunable repetition rate of 20-60kHz. Two amplification stages are followed to boost the average power to 1000W. The waveforms and spectra are captured by an oscilloscope (Lecroy WaveSurfer 44MXs-B) and a spectrograph (YOKOGAWA AQ6370D), respectively. We utilize the homemade 10μm /130μm, 30μm /250μm, and 100μm /400μm DCYDFs to provide the laser gain media in the seed source, preamplifier, and main amplifier, respectively. At the output end, a coreless fiber with a cleaved angle of about 8° is used to mitigate the laser intensity.
Results and Discussion A pulsed power of 2.87W, at a repetition rate of 60kHz, and a pulse width of 150ns, is generated by the Q-switched seed source. After two stages of amplification, the average power is boosted to 1000W, with the pulse width broadened to about 260ns [Fig. 2(a)]. The pulse energy is 16.7mJ and the peak power is about 64kW. Neither SRS nor high-frequency parasitic oscillation appears at the highest power [Fig. 2(b)]. The slope efficiency is about 72.5%. A linearly fitted curve indicates the possibility of further power scaling, but this is limited by pump promotion [Fig. 2(c)].
Conclusion Using homemade DCYDFs, we have demonstrated the realization of a 1000W nanosecond pulsed fiber laser based on an acousto-optic-modulator-based and Q-switched seed source and two stages of amplification. Neither SRS nor parasitic oscillation is generated in the spectra and power scaling is limited by pump promotion. To our knowledge, this is the first kilowatt pulsed fiber laser based on homemade fibers.
